At the end of the nineteenth century, approaches from experimental physiology made inroads into embryological research. A new generation of embryologists felt urged to study the mechanisms of organ formation. This new program, most prominently defended by Wilhelm Roux, was called Entwicklungsmechanik. Named variously as “causal embryology”, “physiological embryology” or “developmental mechanics”, it catalyzed the movement of embryology from a descriptive science to one exploring causal mechanisms. This article examines the specific scientific and epistemological meaning of the mechanistic approaches (...) of embryological development by focusing on Wilhelm His’ histogenetic work. Roux was neither the first, nor the only one to argue for an experimental exploration of causes in embryology. At the time of Roux, physiological explanations of the genesis of the anatomical forms were developing in parallel, not only in German-speaking countries, but in France, Switzerland and English-speaking countries as well. The experimental approach and the cellular descriptions of embryogenesis were already omni-present when Roux proposed his Entwicklungsmechanik. However, these approaches remained disjointed. It appears that it was Wilhelm His who first succeeded in combining the question of the causal factors determining epigenesis, which was closely connected with experimentation on, and cellular descriptions of, development, in a coherent and concrete synthesis, making him one of the true initiators of the developmental mechanics. (shrink)

The conception of “prospective potency” was defined by its author H.Driesch as “the sum of the possible modes of development of a given part of the embryo”. However, in the language of science the word “potency” usually means “power”, not “possibility”. Therefore this conception from the beginning possessed a certain ambiguity, that it retained up to the present. The distinction of “active” and “passive” potency, introduced by Roux, has found no general acceptance. It appeared necessary to submit the conception of (...) “potency” to a profound analysis. In the first place it is shown, that the ambiguity of this conception vanishes, if we understand by the word “potency” those fundamental properties of the embryonic material, that are responsible for its various developmental possibilities. We can distinguish among these properties the “reactive powers”, by which the embryonic material reacts to inductive stimulations, and its own “developmental tendencies”. These faculties only differ by their strength; a “reactive power” may change into a “tendency”, when its intensity increases during development; conversely, a “tendency” may change into a mere “reactive power” by a decrease of its strength. The determination of the material results from the conflict of its tendencies. The inductive actions interfere by strengthening or weakening different tendencies, and by activating new tendencies by reinforcement of the “reactive powers” of the embryonic material. (shrink)

The conception of “prospective potency” was defined by its author H.Driesch as “the sum of the possible modes of development of a given part of the embryo”. However, in the language of science the word “potency” usually means “power”, not “possibility”. Therefore this conception from the beginning possessed a certain ambiguity, that it retained up to the present. The distinction of “active” and “passive” potency, introduced by Roux, has found no general acceptance. It appeared necessary to submit the conception of (...) “potency” to a profound analysis. In the first place it is shown, that the ambiguity of this conception vanishes, if we understand by the word “potency” those fundamental properties of the embryonic material, that are responsible for its various developmental possibilities. We can distinguish among these properties the “reactive powers”, by which the embryonic material reacts to inductive stimulations, and its own “developmental tendencies”. These faculties only differ by their strength; a “reactive power” may change into a “tendency”, when its intensity increases during development; conversely, a “tendency” may change into a mere “reactive power” by a decrease of its strength. The determination of the material results from the conflict of its tendencies. The inductive actions interfere by strengthening or weakening different tendencies, and by activating new tendencies by reinforcement of the “reactive powers” of the embryonic material.La conception de „prospektive Potenz” fut définie par son auteur H.Driesch comme „l'ensemble des modes de développement possibles d'une certaine partie de l'embryon”. Cependant, le, mot „Potenz” dans le langage de la science répond plutôt à la „puissance” qu'à la „possibilité”. De là résulte, que cette conception dès son origine avait une certaine ambiguïté, qui se fait sentir jusqu'à présent. La distinction entre „potentialité active” et „potentialité passive”, proposée par Roux, n'est pas acceptée généralement. Il se trouvait nécessaire, que la conception de „Potenz” fût soumise à une. analyse profonde. D'abord il est démontré, que l'ambiguïté de cette conception disparaît, si on entend par le mot „Potenz” les propriétés fondamentales du matériel embryonnaire, qui sont à la base de ses diverses possibilités de développement. On peut distinguer parmi ces propriétés les „pouvoirs réactifs”, en vertu desquels le matériel embryonnaire répond à des inductions morphogénétiques, et les „tendances propres” du matériel. Ils ne diffèrent que par leur intensité; un „pouvoir réactif” peut se changer en „tendance” par suite d'un renforcement au cours du développement, une „tendance” peut se changer en „pouvoir réactif” par une diminution d'intensité. La détermination du matériel se réalise par une „lutte” entre les tendances. Les actions inductives influent sur cette lutte en renforçant ou en diminuant l'intensité des diverses tendances, et en activant de nouvelles tendances par le renforcement de „pouvoirs réactifs”. (shrink)

“Prizeworthy Research?” Wilhelm Roux and His Program of Developmental Mechanics. The Nobel Prize in physiology or medicine is awarded annually to a maximum of three laureates. Not surprisingly, the number of nominees is much larger. Drawing on Nobel Prize nominations in the Nobel archives in Sweden, the core of this paper deals with the nomination letters for the physiologist Wilhelm Roux to discuss competition and some controversies among German physiologists around 1900 in this particular context. The paper elucidates the arguments (...) brought forward to portray Roux as a scientist who had conferred “the greatest benefit to mankind” in the field of physiology or medicine ; examines some other runners-up, and reconstructs why Roux as well as some of his peers were not awarded the Nobel Prize. On a more general level, we argue that an analysis of Nobel Prize nominations contributes to a broader history of excellence in science and medicine in the twentieth century. (shrink)

In 1956, in his Principles of Embryology, Conrad Hal Waddington explained that the word “epigenetics” should be used to translate and update Wilhelm Roux’ German notion of “Entwicklungsmechanik” to qualify the studies focusing on the mechanisms of development. When Waddington mentioned it in 1956, the notion of epigenetics was not yet popular, as it would become from the 1980s. However, Waddington referred first to the notion in the late 1930s. While his late allusion clearly reveals that Waddington readily associated (...) the notion of epigenetics with the developmental process, in the contemporary uses of the notion this developmental connotation seems to have disappeared. The advent and success of molecular biology have probably contributed to focusing biologists’ attention on the “genetic” or the “non-genetic” over the “developmental”. In the present paper, I first examine the links that exist, in Waddington’s work, between the classical notion of epigenesis in embryology and those of epigenetics that Waddington proposed to connect, and even synthesize, data both from embryology and genetics. Second, I show that Waddington’s own view of epigenetics has changed over time and I analyze how these changes appear through his many representations of the relationships between genetic signals and developmental processes. (shrink)

In biology, the “field” concept is used in different ways. Therefore, its meaning in biology as compared to that in physics, and the relation between the conceptions of “gradient” and “field” are studied.In physics, scalar fields, vector fields and tensor fields are distinguished. In a scalar field, the variation of the scalar in space is expressed in form of a gradient. For the whole of a scalar field with its derived gradients the term “gradient-field” may be used.In biology, especially in (...) experimental embryology, the field concept is used both in a purely descriptive sense and as a means of causal analysis. To the first group belong the kinematic fields and growth fields. The kinematic field is a vector field; the growth field is generally a tensor field, but may be treated as a gradient-field in the most simple cases. In the causal analysis of development the gradient-field plays an important part, in the form of axial, superficial and spatial gradient-fields. In such a field by the combined action of the scalar and the gradients a great diversity of relations may occur. Probably, both the induction field and the organisation field belong to the class of gradient-fields.Der Feldbegriff wird in der Biologie in sehr verschiedener Weise verwendet. Es wird daher versucht, das Wesen der „biologischen Felder” in Anlehnung an die Physik zu bestimmen, und das Verhältnis zwischen den Begriffen „Gradient” und „Feld” darzustellen.In der Physik unterscheidet man Skalarfelder, Vektorfelder und Tensorfelder. Im Skalarfeld lässt sich der Wechsel der Skalargrösse im Raume durch einen Gradienten darstellen. Für die Gesamtheit eines Skalarfeldes mit seinen abgeleiteten Gradienten wird der Ausdruck „Gradientfeld” vorgeschlagen.In der Biologie, im besonderen in der Entwicklungsmechanik, wird der Feldbegriff bald in rein-beschreibendem Sinne, bald als Mittel zur kausalen Analyse verwendet. Zur ersten Gruppe gehören das Bewegungsfeld und das Wachstumsfeld. Das Bewegungsfeld ist ein Vektorfeld; das Wachstumsfeld ist im allgemeinen ein Tensorfeld, kann aber im einfachsten Falle als ein Gradientfeld betrachtet werden. In der kausalen Analyse der Entwicklungserscheinungen spielt besonders das Gradientfeld eine grosse Rolle; dabei kann es sich um ein axiales, oberflächliches oder räumliches Gradientfeld handeln. Es wird darauf hingewiesen, dass in einem Gradientfelde durch das Zusammenwirken der Skalargrösse und des Gradienten eine grosse Mannigfaltigkeit der Beziehungen auftreten kann. Auch das Induktionsfeld und das Organisationsfeld gehören vermutlich zu den Gradientfeldern. (shrink)

For Uexküll, biology is the science of the organization of living beings. In the context of Entwicklungsmechanik, he refers to Driesch’s and Spemann’s experiments on the development of embryonic germ cells to prove that self-differentiating processes constitute organisms as natural objects. Uexküll focuses on the theory of such self-differentiating processes or organizations. The notion of organization implies for him a “technique of nature” that is capable of structuring organic and inorganic material according to plans and rules. These plans and (...) rules are part of the overall order of the world. As preformed sign systems or codes, they determine and regulate the development and existence of individual animal subjects in their specific Umwelten. (shrink)

Early in his career Thomas Hunt Morgan was interested in embryology and dedicated his research to studying organisms that could regenerate. Widely regarded as a regeneration expert, Morgan was invited to deliver a series of lectures on the topic that he developed into a book, Regeneration. In addition to presenting experimental work that he had conducted and supervised, Morgan also synthesized and critiqued a great deal of work by his peers and predecessors. This essay probes into the history of regeneration (...) studies by looking in depth at Regeneration and evaluating Morgan’s contribution. Although famous for his work with fruit fly genetics, studying Regeneration illuminates Morgan’s earlier scientific approach which emphasized the importance of studying a diversity of organisms. Surveying a broad range of regenerative phenomena allowed Morgan to institute a standard scientific terminology that continues to inform regeneration studies today. Most importantly, Morgan argued that regeneration was a fundamental aspect of the growth process and therefore should be accounted for within developmental theory. Establishing important similarities between regeneration and development allowed Morgan to make the case that regeneration could act as a model of development. The nature of the relationship between embryogenesis and regeneration remains an active area of research. (shrink)